Controlled synthesis of 2D Mo₂C/graphene heterostructure on liquid Au substrates as enhanced electrocatalytic electrodes

2D Mo₂C has drawn considerable interest recently for its excellent properties in 2D superconductivity and enhanced hydrogen evolution reaction (HER). Liquid metals have been demonstrated to be an ideal substrate for large-area 2D Mo₂C growth. However, the growth mechanism of 2D Mo₂C on liquid metals has rarely been explored. Here we report the synthesis of high-quality 2D Mo₂C crystals and Mo₂C/graphene heterostructures on liquid Au by chemical vapor deposition method. A sunk growth mode of 2D Mo₂C on liquid Au substrates has revealed, by atomic force microscope characterizations, that some Mo₂C crystals grow below the level of Au terraces around tens of nanometers. Furthermore, graphene/Mo₂C heterostructure is controllably synthesized by tuning the hydrogen/carbon ratio, which is proven to be an enhanced electrocatalyst for HER against pure Mo₂C crystal grown on liquid Au substrates.